Analog Characteristics of Fully Printed Flexible Organic Transistors Fabricated With Low-Cost Mass-Printing Techniques

Abstract

Fully printed organic field effect transistors (OFETs) are fabricated on a flexible, 100-μm-thick, polyethylene terephthalate substrate using high-throughput printing techniques: 1) Cyflex; 2) gravure; 3) screen; and 4) flexographic printing without using a cleanroom, and below 130°C. The dependence of the transconductance g <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> , transit-frequency f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T,</sub> and intrinsic-gain on the bias drain current I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</sub> are measured. The OFETs show intrinsic gain for I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</sub> >10 nA mm (per millimeter width), and reach f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> =64 kHz at I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</sub> = 16 μA/mm, whereas the g <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> loss with frequency is 10% up to f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> . Unlike silicon MOSFETs, the dependence of the OFET g <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> on the f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> in the subthreshold region is found to be weaker than I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1.0</sup> . In addition, the overlap capacitance of the staggered-geometry OFET shows strong frequency dependence, and this is shown to be related to the overlap semiconductor. For the first time, it is found that the impact of process variations and bias stress on the OFET analog characteristics can be significantly attenuated by biasing the device at a fixed I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</sub> . This approach is tested on an array of five amplifiers, reaching the gain-bandwidth product of 32 kHz, within ±3.7% variations.